1. Field of the Invention
The area of the invention is that of turbomachines, and more particularly that of devices allowing air to be discharged at the outlet from a compressor when necessary according to the conditions of use of the turbomachine.
2. Description of the Related Art
Commercial aircraft are generally fitted with bypass turboduct engines which consist of a gas turbine driving a ducted fan which is generally situated upstream of the engine. The mass of air drawn in by the engine is divided into a primary flow, which circulates in the gas turbine or primary body, and a bypass flow which is created by the fan, the two flows being concentric. The primary flow or hot flow leaves the fan to pass into the primary body where it is recompressed, heated in a combustion chamber, guided towards successive stages of turbines and then ejected in a primary gas flow. The bypass flow or cold flow is compressed by the ducted fan stage then ejected directly without having been heated. The two flows can be ejected separately in two concentric flows, or mixed into the same channel before ejection. They separate downstream of the fan at an inter-duct case which surrounds the primary flow and, via its outer part, guides the bypass flow into a cold flow channel.
The primary flow is generally compressed by a first compressor, known as the low pressure (LP) or booster compressor, which is driven by the same LP shaft as the fan, and then guided into a second, high pressure (HP) compressor driven by an HP shaft, before entering the combustion chamber. The two LP and HP shafts are supported on bearings which are situated at the front and rear of the engine and are themselves supported by structural components, known as the intermediate case at the front and as the exhaust case at the rear. With regard to the front part which is shown generically in FIG. 1, the intermediate case is linked to the external structure of the engine by arms which pass through the bypass flow in order to transmit the weight and thrust forces thereon to the aircraft. Conventionally, the arms of the intermediate case are situated axially between the LP compressor and the HP compressor, delimiting three chambers in the inter-duct case: a first chamber, called the fan booster inter-duct case, is situated upstream of said arms and surrounds the LP compressor to separate the primary flow passing into the LP compressor from the bypass flow circulating in the cold flow channel; a second chamber, called the intermediate inter-duct case, guides the primary and bypass flows between the different arms of the intermediate case; finally a third chamber, called the core compartment, surrounds the HP compressor and extends along the engine downstream of the intermediate case arms.
Also, existing engines are generally fitted with devices known as bleed valves or VBV (variable bleed valve) which allow part of the primary flow leaving the LP compressor to return to the cold flow channel, where it mixes with the bypass flow. The effect of this discharge is to lower the operating point of the LP compressor by lowering the pressure downstream, and avoid surge phenomena. The discharge is achieved through openings made in the upper wall of the primary duct between the LP and HP compressors, and by the passage of air taken from a duct which brings it level with an outlet grille situated on the inner wall of the bypass duct, downstream of the diffusers placed in the bypass flow (OGV). The openings can be doors which open like a scoop, by rotating around an axis oriented tangentially to one of the walls of the inter-duct case, or more recently a slot or grille which extends circumferentially and is closed by a so-called guillotine ring moving axially. In both cases, the openings are controlled using arm, pivot or cylinder type mechanisms arranged inside the chambers of the inter-duct case. In the case of door systems, these can be synchronized by a circumferential ring which actuates their opening or closing arms simultaneously. Whatever type of opening is selected, the various actuator elements are generally divided between the three chambers of the inter-duct case, depending on the space available in each.
However, the space available—in particular in the first chamber—is extremely limited and it is very difficult to accommodate part of the mechanism there without deforming the profile of the inter-duct case, which would have an effect on the aerodynamic flow of the primary and bypass ducts. Similarly, the cylinders which actuate this mechanism are relatively bulky and must generally be placed in the third chamber, which may already contain a substantial amount of equipment.
In this case, the proximity of these cylinders to the HP compressor means that cylinders with a cooling system must be used, which increases their volume further.
It is therefore desirable to design control devices for the LP compressor bleed valves which are relatively compact and can substantially be accommodated in the first or second cavity of the inter-duct case.